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• ALLUVIAL GROUNDWATER HYDROLOGY <br />OF THE NORTH FORK OF THE GUNNISON RIVER <br />BEAR N0. 3 OPERATION <br />The planned surface facilities at the Bear No. 3 Operation are located <br />in the valley along the North Fork of the Gunnison River. The alluvium <br />consists of course sand, cobbles and boulders derived from igneous and <br />metamorphic rocks in the headwaters and upper reaches of the canyon. <br />Overlying the alluvium is a dark, clayey loam soil and material left <br />over from earlier mining activity consisting of coal, rubble and fill <br />material. The surface facilities will be sited on the south bank of the <br />river, in the interior of a right meander in which the river has become <br />entrenched. <br />The alluvium is saturated to a level approximately four feet below the <br />surface. To determine the depth of the water table and to facilitate <br />groundwater sampling, three alluvial wells were installed in backfilled <br />• pits dug with a backhoe. The lithology, soil and root depths of the <br />three backhoe pits (designated Alluvial Aquifer (AA) 1, 2 and 3) are <br />shown on the attached logs. In addition, four older drill holes were <br />located in the surface facilities area. Three are cased wells used for <br />domestic water supply. The well used for water level measurement are <br />shown on the attached map. The map illustrates the elevation and extent <br />of the water table and direction of groundwater flow in the alluvium. <br />To document flow rates, yield and permeability of the alluvial aquifer, <br />a pump test was performed on the supply well to the mine office on <br />February 13, 1982. The office well was pumped at an average rate of 6.2 <br />gallons per minute for 100 minutes. The data collected during the test <br />is listed in the attached table. Total adjusted drawdown was 2.81 feet. <br />Specific yield of the well is calculated to be 2.2 gallons per minute <br />per foot of drawdown. The effective yield of the well, which is 8.7 <br />feet deep, should be approximately 10.5 gallons per minute for domestic <br />• use. The drawdown vs. time plot derived from the test data was applied <br />to the Theis type curve for unconfined aquifers as demonstrated in USGS <br />